Cannot delete bootcamp partition/free space on HD (OS X Mavericks)

Question

I am having trouble removing a bootcamp partition made a while ago. I thought removing this partition would be as simple as using disk utility to delete the partition, and extend the Macintosh HD partition back to its original size.
However, after clicking the minus sign using disk utility I am now left with 51.24GB free space where the bootcamp partition used to be and cannot seem to do anything to bring the hard drive back to one single partition.
I have tried using boot camp assistant, which is useless. I have to tick either "Install Windows 7" or "Download the latest Windows support software from Apple", and when I click to install windows 7 (which below says it can be used to remove an existing windows partition), it only lets me re-size the Windows partition to a smaller 20GB size. It does not give me the option to remove the partition like it says it does on the first page and like I have seen on examples online (which I am sure are from previous OS X versions).
I have tried going to disk utility when booting from the recovery disk, however this does not give me the option to erase the entire disk then start again from a time machine backup; it only gives me the option to erase my current 268.48GB Macintosh HD partition, which wouldn't be any use.
I have verified the disk and all seems ok. I am running OS X 10.9.1 on a mid 2010 Macbook Pro. 2.4 GHz Intel Core 2 Duo, 4 GB Memory.
Any help appreciated as I am running low on HD space on my mac and the extra 50 GB that I can't seem to free up would be very useful.

Answer 1

Give this a try:
Install Mavericks, Lion/Mountain Lion Using Internet Recovery
Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.
Boot to the Internet Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND-OPTION- R keys until a globe appears on the screen. Wait patiently - 15-20 minutes - until the Recovery main menu appears.
Partition and Format the hard drive:
1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your external hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed. Quit DU and return to the main menu.
Reinstall Lion/Mountain Lion. Mavericks: Select Reinstall Lion/Mountain Lion, Mavericks and click on the Install button. Be sure to select the correct drive to use if you have more than one.
Note: You will need an active Internet connection. I suggest using Ethernet
            if possible because it is three times faster than wireless.
This will install the default version of OS X that came with your computer if it came with Lion or later. If it came with Snow Leopard, then you must do this instead:
Clean Install of Snow Leopard
Be sure to make a backup first because the following procedure will erase
the drive and everything on it.
     1. Boot the computer using the Snow Leopard Installer Disc or the Disc 1 that came
         with your computer.  Insert the disc into the optical drive and restart the computer.
         After the chime press and hold down the  "C" key.  Release the key when you see
         a small spinning gear appear below the dark gray Apple logo.
     2. After the installer loads select your language and click on the Continue
         button. When the menu bar appears select Disk Utility from the Utilities menu.
         After DU loads select the hard drive entry from the left side list (mfgr.'s ID and drive
         size.)  Click on the Partition tab in the DU main window.  Set the number of
         partitions to one (1) from the Partitions drop down menu, click on Options button
         and select GUID, click on OK, then set the format type to MacOS Extended
         (Journaled, if supported), then click on the Apply button.
     3. When the formatting has completed quit DU and return to the installer.  Proceed
         with the OS X installation and follow the directions included with the installer.
     4. When the installation has completed your computer will Restart into the Setup
         Assistant. Be sure you configure your initial admin account with the exact same
         username and password that you used on your old drive. After you finish Setup
         Assistant will complete the installation after which you will be running a fresh
         install of OS X.  You can now begin the update process by opening Software
         Update and installing all recommended updates to bring your installation current.
Download and install Mac OS X 10.6.8 Update Combo v1.1.